1. Field of the Invention
The present invention relates to antenna systems. More specifically, the present invention relates to single mirror, dual axis beam waveguide antenna systems.
2. Description of the Related Art
A large aperture antenna is used for satellite communications. Such antennas are generally of the fully steerable type, whereby a communication satellite can be tracked anywhere in the sky.
Various mount systems have been developed for driving such a large aperture antenna. For example, the Jet Propulsion Laboratory employs a large aperture array in its deep space network (DSN). It will be appreciated that the DSN antennas transmit an enormous amount of power due to the extremely long communication distances, e.g., Earth to Jupiter. Because of the large transmitters employed, it is impractical to mount the transmitter on the back of the antenna. Moreover, due to the high power involved, conventional waveguide rotary joints are not feasible. Thus, four-mirror beam waveguide antenna feeds are used in high power space communication systems such as the DSN. A beam waveguide antenna feed is a system that employs a series of mirrors, allowing a reflector antenna to be rotated about one or more axis, while keeping the feed horn and transmitter stationary. Typical systems are disclosed in U.S. Pat. No. 4,044,361 and U.S. Pat. No. 4,186,401, which patents are incorporated herein by reference. These types of beam-waveguide systems are most commonly encountered in high-performance aerial systems, where easy access to the transmitting and receiving equipment is a desirable feature.
One of the drawbacks of multiple mirror arrangements, such as four-mirror beam waveguide antenna feeds, relates to alignment. The more mirrors in a beam waveguide system, the more complicated it is to not only initially align the mirrors, but to maintain alignment over long periods of time.
For a stationary communication system such as the DSN system, the alignment of a beam waveguide system can be maintained. However, some high power systems are required to be portable. The designers of some portable high power systems have not used beam waveguide systems for the specific reason that the mirrors would become misaligned while the system is being transported.
Another drawback of the multiple mirror arrangements relates to power loss. Each mirror contributes a small amount of loss to the microwave beam due to conduction and diffraction. Thus, more mirrors lead to more power loss.
What is needed is a beam waveguide system which uses fewer mirrors. What is also needed is a portable beam waveguide system having improved alignment stability. It would be desirable if the portable beam waveguide system were suitable to a broad spectrum of antenna designs. What is also needed is a dual-axis beam waveguide antenna system wherein the axes of rotation are located near the center of gravity of the main reflector antenna, allowing for a lighter-weight gimbaling system.